GLASS, ESPECIALLY AS A COVER

- Schott AG

A chemically temperable or chemically tempered glass includes SiO2, Al2O3, Li2O and B2O3 as constituents. The following applies for the constituents (in mol % based on oxide): 0.8<Li2O/(Li2O+K2O+Na2O)≤1 and 0.1<B2O3≤8.5.

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Description
CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to German Patent Application No. 10 2023 124 136.2 filed on Sep. 7, 2023, which is incorporated in its entirety herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a chemically temperable or chemically tempered glass, to a process for the production thereof, to a cover made of such a glass and the use thereof and to a digital display device comprising such a cover.

2. Description of the Related Art

The use of glass or glass ceramics as covers for electronic components and displays, in particular for smartphones, has long been known. These glass-based materials are optionally chemically tempered to increase their mechanical strength.

Glasses made of the Li2O—Al2O3—SiO2 system, so-called LAS glasses, have proven particularly suitable here. They comprise SiO2 and Li2O and Al2O3 as primary components. LAS glasses include the subgroup of boron-containing LAS glasses, also known as LABS glasses.

Compared to AS glasses, i.e. Li-free glasses, especially having regard to their use as cover materials, LABS glasses have the advantage that they are very readily chemically temperable through ion exchange of Li ions for Na ions or through combined ion exchange, namely Li ions for Na ions and Na ions for K ions, and thus have a high mechanical strength both against so-called “sharp impact stresses”, i.e. against the influence of rough surfaces and sharp objects, and against the influence of blunt or smooth surfaces, so-called “blunt impact stresses”. LABS glasses are preferred compared to LAS glasses since the addition of B2O3 results in stronger bonding of the glass network and further improved mechanical properties, such as scratch resistance.

Such glasses are known from the prior art.

Thus, U.S. Patent Application Publication No. 2017/197869 A describes LABS glasses which, according to the examples, have a relatively high coefficient of expansion and have a low Li2O proportion in the total content of alkali metal oxides.

U.S. Patent Application Publication No. 2018/186685 A also describes LABS and LAS glasses. Especially the LABS glasses have a low Li2O proportion in the total content of alkali metal oxides.

U.S. Patent Application Publication No. 2018/127302 A describes LABS glasses having rather low Li2O contents based on the total alkali metal oxide content and/or high boron contents.

U.S. Patent Application Publication No. 2020/317558 A describes AS, i.e. Li-free, glasses or LA (B) S glasses, wherein these have rather low Li contents and/or lack B2O3.

German Patent Application No. 10 2019 121 146 A describes LAS glasses having a minimum content of the nucleating agents ZrO2, SnO2 and TiO2.

German Patent Application No. 10 2019 121 143 A describes LAS glasses having rather high contents of alkali metal oxide, especially Na2O.

What the different glasses of the prior art having the abovementioned good product properties have in common is that they are difficult to process. This concerns the behaviour not only of the glass melt in the refining zone but also of the glass during shaping and cooling, as well as its susceptibility to crystallization.

What is needed in the art is a way to provide a chemically temperable or tempered glass, especially for use as cover glass, which, on account of its viscosity properties, is easily fusible, refinable and hot-formable and is economic to produce. The glass shall naturally also exhibit the product properties necessary for its intended use in the tempered state.

What are also needed are a process for producing such a glass and to a cover made of such a glass and the use thereof and to a digital display device comprising such a cover.

SUMMARY OF THE INVENTION

In some embodiments provided according to the invention, a chemically temperable or chemically tempered glass includes SiO2, Al2O3, Li2O and B2O3 as constituents. The following applies for the constituents (in mol % based on oxide): 0.8<Li2O/(Li2O+K2O+Na2O)≤1 and 0.1<B2O3≤8.5.

In some embodiments provided according to the invention, a process for producing a tempered glass is provided. The glass includes SiO2, Al2O3, Li2O and B2O3 as constituents. The following applies for the constituents (in mol % based on oxide): 0.8<Li2O/(Li2O+K2O+Na2O)≤1 and 0.1<B2O3≤8.5. The method includes: producing the glass by a melting process, a refining of a glass melt produced during the melting process, and a subsequent hot forming; and performing at least one ion exchange in an exchange bath having a composition of 100% by weight to 0% by weight of KNO3 and 0% by weight to 100% by weight of NaNO3 and 0% by weight to 5% by weight of LiNO3 at a temperature of the exchange bath between 370° C. and 500° C. and a duration between 1 hour and 50 hours.

In some embodiments provided according to the invention, a cover includes a tempered glass having a thickness of 0.3 mm to 1 mm. The glass includes SiO2, Al2O3, Li2O and B2O3 as constituents. The following applies for the constituents (in mol % based on oxide): 0.8<Li2O/(Li2O+K2O+Na2O)≤1 and 0.1<B2O3≤8.5.

DETAILED DESCRIPTION OF THE INVENTION

The chemically temperable or chemically tempered glass provided according to the invention comprises the constituents SiO2, Al2O3, Li2O and B2O3 and optionally Na2O and optionally K2O. The following applies for the B2O3 content (in mol % based on oxide): 0.1<B2O3≤8.5; optionally 0.1<B2O3<8.5.

The recited minimum content of B2O3 is necessary for a low upper devitrification limit. The upper devitrification limit is the temperature at which the glass is free from crystals after heating from room temperature and holding for one hour. LABS glasses generally crystallize upon heating in a temperature range above the glass transition temperature Tg. If the temperature is further increased, the crystals redissolve. Since the dissolution may proceed slowly due to the viscosity of the glass, the temperature is held for 1 h. The upper devitrification limit is a measure of the susceptibility of a glass to crystallization. If said limit is low, this advantageously means that the glass is less prone to crystallization (the crystals are rather “unstable” and dissolve even at low temperatures) and is therefore also more readily producible. Contents higher than the recited contents of B2O3 can result in demixing and are disadvantageous for ion diffusion, especially of K ions.

The following applies for the alkali metal oxides Li2O, Na2O and K2O (all contents in mol %): 0.8<Li2O/(Li2O+K2O+Na2O)≤1. This condition can be met by the presence of all three recited alkali metal oxides or of Li2O together with K2O or with Na2O or else by the sole presence of Li2O (Li2O/(Li2O+K2O+Na2O)=1). A ratio of Li2O/(Li2O+K2O+Na2O)<1 may be preferred.

The chemically temperable or chemically tempered glass provided according to the invention has an upper devitrification temperature OEG which is less than 10 K above the processing temperature VA, optionally below it. This makes it possible to avoid uncontrolled crystallization of undesired crystal phases, for example spodumene, keatite, forsterite, baddeleyite, gahnite, during the production process, in particular during the hot forming.

The processing temperature VA, i.e. the temperature at a viscosity of 104 dPas, may by preference be less than 1300° C., optionally less than 1260° C., particularly optionally less than 1220° C. This facilitates shaping and especially makes it possible to establish a low homogeneous glass thickness, especially in a float bath.

The glass has a temperature at a viscosity of 102 dPas, known as T2, of at most 1800° C., optionally of less than 1750° C., optionally of less than 1720° C. As a result, the glass is readily refinable and, as a product, exhibits good optical quality without gas inclusions, i.e. without scatter.

The glass has a coefficient of thermal expansion CTE20-300 of less than 5.4 ppm/K. This allows stress-free cooling after the hot-forming process. The glass optionally has a coefficient of thermal expansion CTE20-300 of more than 3.8 ppm/K.

The glass provided according to the invention having the specified properties may be realized via a LABS glass having a composition comprising the specified features 0.1<B2O3≤ 8.5 and 0.8<Li2O/(Li2O+K2O+Na2O)≤1.

The glass optionally exhibits good chemical resistances both in the untempered state and in the tempered state, namely:

    • a hydrolytic resistance H according to DIN 52296: Glass and glass ceramics: Hydrolytic resistance of the surface of glass and glass ceramic plates at 98° C.,
    • method of test and classification (modification: determination of additional cations with ICP) (1989-12);
    • an alkali resistance L according to DIN ISO 695: Glass: Resistance to attack by a boiling aqueous solution of mixed alkali, method of test and classification (1994 02);
    • and an acid resistance S according to DIN 12116: Testing of glass-Resistance to attack by a boiling aqueous solution of hydrochloric acid, method of test and classification (2001 03);
    • of class 3 or better in each case.

In the context of the present disclosure the constituents of the glass are reported in mol % based on oxide.

In some embodiments, the proportions of these constituents in mol % based on oxide are:

    • SiO2 62-72, optionally 65-70,
    • and/or
    • Al2O3 7-14, optionally 8-12,
    • and/or
    • B2O3 0.1-8.5, optionally <8.5 or ≤8, optionally 4-7, optionally ≥5, optionally>5.5,
    • and/or
    • Li2O 5-12, optionally 7-10,
    • and/or
    • Na2O 0-2, optionally 0-1, optionally ≥0.1 and/or <1, optionally ≥0.3 and/or <0.8, and/or
    • K2O 0-2, optionally 0-1.

The presence of SiO2, optionally at a minimum content of 62 mol % or even 65 mol %, is necessary for the formation of a stable glass network, which increases mechanical and chemical resistance. SiO2 increases the viscosity of the melt. Excessive levels should be avoided to allow fusibility and to have a sufficiently low viscosity for ascending of bubbles during refining. The maximum content thereof is therefore optionally limited to 72 mol %, particularly optionally to 70 mol %.

The presence of Al2O3, optionally at a minimum content of 7 mol % or even 8 mol %, is necessary to allow rapid alkali diffusion in the glass and high compressive stresses (CS30 and CS50 values). At excessive Al2O3 contents the crystallization propensity of the glass increases markedly. The maximum content thereof is therefore optionally limited to 14 mol %, particularly optionally to 12 mol %.

The presence of B2O3, optionally at a minimum content of 4 mol % or 5 mol % or more than 5 mol % or even of 5.5 mol % or more than 5.5 mol %, has a positive effect on fusibility. Contents above the exemplary upper limit of 8.5 mol % can already lead to a slight decrease in chemical resistance and CS30 and CS50 values. The B2O3 content is therefore optionally limited to less than 8.5 mol % or to at most 8 mol %, optionally to at most 7 mol %.

The presence of Li2O, optionally at a minimum content of 5 mol %, optionally at a minimum content of 7 mol %, allows chemical tempering of the glass in a sodium-containing salt bath. The content thereof is optionally limited to 12 mol %, optionally to 10 mol %, since otherwise the crystallization propensity increases markedly, especially with precipitation of Li2O-containing (and Al2O3-containing) crystal phases such as for example spodumene or keatite.

If Na2O is present, optionally at a content of at least 0.1 mol %, optionally at at least 0.3 mol %, this may be advantageous for the fusibility and inhibits crystallization. Due to the adverse effect on compressive stresses (CS30 and CS50 values) and the increase in the thermal coefficient of expansion, its maximum content is optionally limited to 2 mol %, optionally to 1 mol %, and optionally to less than 1 mol %.

If K2O is present this has a positive effect on fusibility. K2O additionally increases K diffusion in the glass and allows for a deeper tempering (K-DoL) in the last tempering step in multi-stage tempering. The K2O content is optionally limited to 1 mol % since excessively high K2O contents have an adverse effect on the K-induced tempering (KCS).

In some embodiments, the glass may comprise the following constituents (in mol % based on oxide):

    • MgO 0-5, optionally 0.5-3,
    • and/or
    • CaO 0-8, optionally 1-6,
    • and/or
    • SrO 0-5, optionally 0-1,
    • and/or
    • BaO 0-2,
    • and/or
    • ZnO 0-5, optionally 0-1,
    • and/or
    • P2O5 0-5, optionally 0.5-2,
    • and/or
    • ZrO2 0-5, optionally 0-3.

Alkaline earth metal oxides and/or ZnO may be used to reduce the viscosity of the glass and thus improve manufacturability.

If ZnO is present, the content thereof is optionally limited to 5 mol %, optionally to 1 mol %, since higher contents can result in evaporation during the melting process and thus in corrosion of the refractory material in glass production.

If MgO is present, optionally at a minimum content of 0.5 mol %, this has a positive effect on fusibility. Contents above 5 mol % favor crystallization and are thus optionally avoided. In some embodiments the content is therefore also limited to at most 3 mol %.

If CaO is present, optionally at a minimum content of 1 mol %, this favors the desired low upper devitrification temperature OEG.

If SrO is present the content thereof is optionally limited to 5 mol %, optionally to 1 mol %, since higher contents result in a reduction in alkali metal diffusion in the glass during chemical tempering with the result that very long tempering times become necessary or only low DoCL values are achievable.

If BaO is present the content thereof is optionally limited to 2 mol %. It may be preferable when the glass is substantially free from BaO.

If P2O5 is present, optionally with a minimum content of 0.5 mol %, this has a positive effect on alkali metal diffusion in the glass. This is advantageous because the duration of ion exchange can be shortened. The P2O5 content should optionally not exceed 5 mol %, optionally 2 mol %, since excessively high contents may lead to corrosion of the refractory material in glass production.

If ZrO2 is present this has a positive effect on the chemical resistance of the glass. However, high contents of ZrO2 promote devitrification. The maximum content thereof is thus optionally limited to 5 mol %, optionally to 3 mol %, optionally to 2 mol % or even to only 1 mol %.

The glass may also contain TiO2 for example. If TiO2 is present the content thereof is optionally limited to 2 mol %. It may be preferable when the glass is substantially free from TiO2.

The term “substantially free” is to be understood as meaning that only impurities that are unavoidable in customary and economic methods (for example due to raw materials) are present.

Certain relationships between the components have proven highly advantageous for the glass and its manufacturability and chemical temperability. The composition thereof is thus optionally chosen such that the following applies for the constituents (in mol % based on oxide):

    • 0.9<(Al2O3+B2O3+ZrO2)/(R2O+RO)<1.7;
    • optionally 1<(Al2O3+B2O3+ZrO2)/(R2O+RO)<1.6;
    • optionally 1.1<(Al2O3+B2O3+ZrO2)/(R2O+RO)<1.5;
    • and/or
    • 0.5<Al2O3/(R2O+RO)<1.1;
    • optionally 0.6<Al2O3/(R2O+RO)<0.9;
    • optionally 0.7<Al2O3/(R2O+RO)<0.85;
    • wherein R2O=Li2O+K2O+Na2O and
    • RO=MgO+CaO+SrO+BaO+ZnO.

A ratio of 0.5<Al2O3/(R2O+RO)<1.1 is advantageous for glass formation.

If the Al2O3/(R2O+RO) ratio is greater than 1.1, the crystallization propensity to form Al2O3-containing crystals increases markedly since there is insufficient R2O and RO to “dissolve” all of the Al2O3 in the glass. At an Al2O3/(R2O+RO) ratio of less than 0.5 an excessive amount of non-bonding bridging oxygens is present and the alkali metal diffusion is reduced since the negative charges are concentrated on individual oxyanions and are no longer delocalized over a whole AlO4 tetrahedron. This leads to stronger electrostatic bonding of the mobile alkali metal cations to the glass matrix and the chemical temperability suffers.

A ratio of 0.9<(Al2O3+B2O3+ZrO2)/(R2O+RO)<1.7 has a positive effect on the connectivity of the glass network and thus on the mechanical stability. Such a ratio also ensures that boron cations are optionally coordinated trigonally with oxygen and not as tetragonal BO4 units. Tetragonal BO4 units have a marked adverse effect on alkali metal diffusion, especially of potassium cations.

In some embodiments the glass may contain 0 to 1 mol % of SnO2, optionally 0.1 to 0.5 mol % of SnO2, and/or 0 to 1 mol % of CeO2 and/or 0 to 1 mol % of Cl, wherein the sum of CeO2+SnO2+Cl is optionally at most 2 mol %.

In some embodiments the glass may contain up to 2 mol %, optionally up to 1 mol %, of the customary refining agents such as As2O3, Sb2O3, SnO2, CeO2, halides, optionally chlorides, or sulfur-containing compounds. For reasons of environmental protection and occupational health and especially also when produced in the float process, the glass is optionally substantially free from arsenic and antimony. This also applies to other toxic or environmentally harmful components, for example PbO, TeO2, CdO.

Especially when it is to be used as a front cover, the glass is also optionally substantially free from coloring components, especially free from coloring rare earths, in particular Nd2O3, Er2O3, and coloring metal oxides, in particular V2O5, CoO, NiO, Cr2O3, CuO.

At a thickness of 0.6 mm such a colorless glass optionally has an average transmittance in the range from 365 to 640 nm of at least 85%.

Especially if the glass is to be used as a back cover it optionally contains coloring components, for example at least 0.1 mol % and at most 5 mol % of at least one coloring component, especially optionally selected from the group of CoO, Fe2O3, TiO2, Cr2O3 and/or MnO and/or mixtures thereof.

The iron content of the glass, reported as a percentage by weight of Fe2O3, should optionally be less than 1000 ppm, particularly optionally less than 500 ppm, to avoid undesired coloring of the material. The iron content of the glass is thus a consequence of unavoidable impurities in the raw materials. The use of low-iron raw materials makes it possible to reduce the amount of iron and thus achieve a better (more neutral) intrinsic color of the glass, though this is generally associated with higher raw material costs.

The glass provided according to the invention is suitable for producing a cover in electronic devices for example, in particular in electronic display devices, in particular in mobile electronic display devices, for example in mobile touch panels and/or mobile digital display devices such as smartphones or smartwatches and generally touch panels.

The cover optionally has a thickness of 0.3 mm to 1 mm, optionally 0.35 mm to 0.7 mm, optionally 0.4 mm to 0.65 mm.

The process for producing a glass comprises the steps of:

    • producing a silicatic glass by a melting process and
    • refining the glass melt and
    • subsequently hot forming.

The hot forming can be carried out, without limiting generality, for example by a drawing process, in particular a float process or a down-draw process, for example an overflow fusion or a drawing nozzle process.

To produce a tempered glass, in particular in embodiments for use as a cover, the above steps are followed by the following step:

    • performing at least one ion exchange in an exchange bath having a composition of 100% by weight to 0% by weight of KNO3 and 0% by weight to 100% by weight of NaNO3 and 0% by weight to 5% by weight of LiNO3 at a temperature of the exchange bath between 370° C. and 500° C. and a duration between 1 hour and 50 hours.

A further possibility is performing an ion exchange in more than one exchange bath, for example initially performing an ion exchange in an exchange bath having a composition of 50% by weight to 0% by weight of KNO3 and 50% by weight to 100% by weight of NaNO3 and 0% by weight to 5% by weight of LiNO3 at a temperature of the exchange bath between 370° C. and 500° C. and a duration between 1 hour and 20 hours and then performing a further ion exchange in an exchange bath having a composition of 100% by weight to 50% by weight of KNO3 and 0% by weight to 50% by weight of NaNO3 and 0% by weight to 5% by weight of LiNO3 at a temperature of the exchange bath between 370° C. and 500° C. and a duration between 1 hour and 20 hours.

Ion exchange in three or more exchange baths is also possible.

The cover made of tempered glass is a high-strength cover.

The high proportion of Li2O in the total alkali metal content of the LABS glass, expressed by Li2O/(Li2O+K2O+Na2O)>0.8, makes it possible even at low glass thickness to achieve good stress values in the tempering process, i.e. high stresses CS not only at the surface but also near the surface, namely CS30>100 MPa, and near the depth of the compressive stress zone, namely CS50>80 MPa, and a deep compressive stress zone DoCL, namely DoCL>0.17*t, wherein t is the thickness of the pane.

Here, CS30, reported in MPa, is the compressive stress at a distance of 30 μm from the surface of a main face, CS50, reported in MPa, is the compressive stress at a distance of 50 μm from the surface of the same main face and DoCL, reported in μm similarly to the thickness of the pane, is the depth of the compressive stress zone of the same main face.

The main faces are those of the glass pane that are the largest in terms of their surface area compared to the other faces. In addition to the two main faces a pane optionally comprises four faces joining the two main faces which are referred to as edge faces. In the case of non-rectangular panes the pane may also have fewer edge faces, for example only one edge face.

The tempering process is a chemical tempering which is optionally carried out by immersing the pane in an exchange bath but may also be carried out by application of pastes to the pane.

An exchange bath is to be understood as meaning a salt melt, wherein this salt melt is used in an ion exchange process for a glass or a glass article. In the context of the present disclosure the terms exchange bath and ion-exchange bath are used synonymously.

Exchange baths generally employ technical-purity salts. This means that, despite the use of, for example, only sodium nitrate as the starting material for an exchange bath the exchange bath still comprises certain impurities. The exchange bath is a melt of a salt, that is to say for example of sodium nitrate, or a mixture of salts, for example a mixture of a sodium salt and a potassium salt. The composition of the exchange bath is reported such as to refer to the nominal composition of the exchange bath without taking into account any impurities present. If in the context of the present invention reference is made to a 100% sodium nitrate melt this is accordingly to be understood as meaning that only sodium nitrate was used as raw material. However, the actual sodium nitrate content of the exchange bath may differ therefrom and will indeed generally do so since especially technical grade raw materials comprise a certain proportion of impurities. However, this is generally less than 5% by weight, based on the total weight of the exchange bath, in particular less than 1% by weight.

Similarly, in the case of exchange baths comprising a mixture of different salts it is generally the nominal contents of the salts that is reported without taking into account impurities resulting from technical grade starting materials. An exchange bath comprising 90% by weight of KNO3 and 10% by weight of NaNO3 may thus likewise comprise a low level of impurities which, however, are a consequence of the raw materials and should generally be less than 5% by weight based on the total weight of the exchange bath, in particular less than 1% by weight.

The composition of the exchange bath also changes in the course of the ion exchange since especially lithium ions migrate out of the glass/the glass article into the exchange bath as a result of ongoing ion exchange. However, such a change in the composition of the exchange bath due to ageing is likewise not taken into account in this case, unless otherwise stated explicitly. On the contrary, in the context of the present disclosure the reported composition of an exchange bath refers to the nominal original composition.

The invention will now be more particularly elucidated by reference to examples.

The compositions of examples of glasses provided according to the invention are reported in Table 1 (all amounts in mol % based on oxide). The compositions of comparative glasses (designations beginning with V) are reported in Table 2 (all amounts in mol % based on oxide).

The materials specified in Tables 1 and 2 were melted and refined using raw materials customary in the glass industry at temperatures from 1550° C. to 1680° C. Melting of the mixture was initially carried out in a Pt/Rh crucible at 1550° C. to 1620° C. The melt was then refined at 1650° C. to 1680° C. and then homogenized by stirring for 30 minutes. After standing at 1550° C. to 1650° C. for 2 h, castings of about 140 mm×100 mm×30 mm in size were cast and annealed at about 500° C. to 650° C. in a lehr and then cooled to room temperature. The cast pieces were used to prepare the test specimens for measuring the properties in the untempered state. The samples for the tempering tests had a thickness of about 0.5 mm.

Tables 1 and 2 report the following properties both for the glasses provided according to the invention and for the comparative glasses:

    • the coefficient of thermal expansion CTE20-300, determined by dilatometry and specified in ppm/K;
    • the glass transition temperature Tg determined by dilatometry and reported in ° C.;
    • the temperature at a viscosity 102 dPas, referred to as T2, reported in ° C. and calculated from the Vogel-Fulcher-Tammann (VFT) equation;
    • wherein the VFT curve describes the decadic logarithm of the viscosity by means of three parameters A, B and TO as a function of temperature T:

lg ⁢ ( ❘ "\[LeftBracketingBar]" η ❘ "\[RightBracketingBar]" ) = A + B / ( T - T ⁢ 0 )

    • wherein VFT parameters (A, B, T0) are determined by fitting the measurement data of viscosity vs. temperature using the VFT function;
    • the density ρ, reported in g/cm3;
    • the temperature at a viscosity 104 dPas, referred to as processing temperature VA, reported in ° C. and determined using a stirring viscometer;
    • the temperature at a viscosity 103 dPas, referred to as T3, reported in ° C. and determined using a stirring viscometer;
    • the upper devitrification temperature, referred to as the OEG, reported in ° C. and determined by gradient tempering. Glass grit is placed on a platinum carrier in a gradient furnace and tempered for one hour. The platinum carrier with the glass is then removed. The temperature at the hot end of the gradient, above which the glass is crystal-free, is referred to as the upper devitrification temperature. The glass samples are inspected for crystals using an optical microscope.

The decadic logarithm of the liquidus viscosity, referred to as lg, reported in dPa*s is the viscosity at the upper devitrification temperature and is determined from the VFT parameters A, B, TO and the OEG according to lg (|η|)=A+B/(OEG−T0).

The abbreviation “n.d.” in the table stands for “not determined”.

Working Examples

TABLE 1 Composition [mol %] 1 2 3 4 5 6 7 8 9 10 11 12 13 SiO2 71.25 68.45 67.75 68.25 68.05 68.05 67.75 67.75 67.75 68.45 67.55 67.95 67.25 Al2O3 8.50 11.00 11.00 11.00 11.00 11.00 11.00 11.00 11.50 11.00 11.40 11.00 11.40 B2O3 8.00 4.00 7.00 6.60 6.60 6.60 6.60 6.60 5.80 4.00 5.70 5.80 5.70 Li2O 8.00 8.00 8.00 8.20 8.20 8.20 8.20 8.20 8.20 8.00 8.20 8.70 8.20 Na2O 0.70 0.70 0.70 0.70 0.70 0.70 0.70 0.40 0.70 0.70 0.70 0.70 0.70 K2O 0.20 0.20 0.20 0.20 0.20 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 MgO 1.00 1.50 1.00 1.00 0.50 0.50 0.50 0.50 0.70 1.00 1.10 0.50 1.40 CaO 0.50 4.30 2.50 2.50 3.20 2.90 2.90 3.20 3.00 4.50 3.00 3.00 3.00 SrO BaO ZnO 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 P2O5 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 Fe2O3 TiO2 ZrO2 0.40 0.40 0.40 0.10 0.10 0.10 0.40 0.40 0.40 0.40 0.40 0.40 0.40 CeO2 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 SnO2 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 SO3 F Cl 0.55 0.55 0.55 0.55 0.55 0.55 0.55 0.55 0.55 0.55 0.55 0.55 0.55 Properties 1 2 3 4 5 6 7 CTE20-300 4.33 4.76 4.55 4.61 4.68 4.76 4.76 [ppm/K] Tg [° C.] 557 596 588 580 586 577 585 T2 (from 1799 1693 1680 1702 1702 1705 1687 VFT) [° C.] ρ [g/cm3] 2.3134 2.4056 2.3593 2.3549 2.3613 2.3581 2.367 VA [° C.] 1242 1219 1214 1227 1220 1215 1212 T3 [° C.] 1465 1412 1405 1422 1417 1414 1407 VFT A −1.994 −2.373 −2.555 −2.584 −2.467 −2.325 −2.532 VFT B 6670.3 6597.9 6962.8 7171.5 6958.7 6700.9 7017.7 VFT T0 129.0 184.0 151.5 137.4 144.5 155.3 138.2 OEG [° C.] 1235 1225 1205 1230 1185 1185 1195 lg (Liquidus 4.04 3.97 4.05 3.98 4.22 4.18 4.11 Viscosity) [dPa*s] Properties 8 9 10 11 12 13 CTE20-300 4.67 4.77 4.9 4.78 4.91 n.d. [ppm/K] Tg [° C.] 586 593 589 595 581 n.d. T2 (from 1682 1687 1688 1678 1689 n.d. VFT) [° C.] ρ [g/cm3] 2.3684 2.375 2.4053 2.38 2.3758 n.d. VA [° C.] 1212 1223 1215 1216 1208 n.d. T3 [° C.] 1404 1413 1408 1406 1404 n.d. VFT A −2.494 −2.590 −2.399 −2.598 −2.382 n.d. VFT B 6849.5 7024.7 6654.5 7006.2 6728.1 n.d. VFT T0 157.6 156.7 175.2 154.0 153.8 n.d. OEG [° C.] 1195 1205 1185 1190 1210 n.d. lg (Liquidus 4.11 4.11 4.19 4.16 3.99 n.d. Viscosity) [dPa*s]

Comparative Examples

TABLE 2 Composition [mol %] V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 V11 V12 V13 V14 V15 SiO2 68.96 69.51 66.51 66.09 68.09 67.09 63.22 68.88 67.68 70.98 68.65 68.65 68.45 68.95 73.40 Al2O3 10.44 10.00 13.00 13.00 11.00 11.00 15.10 11.00 11.50 8.50 11.00 11.00 11.00 11.00 11.50 B2O3 3.60 3.80 3.80 3.80 3.80 3.80 4.00 4.00 3.00 4.00 4.60 4.60 4.60 3.60 Li2O 8.45 8.70 8.70 8.70 8.70 8.70 9.70 8.00 8.00 8.00 8.20 8.20 8.20 8.20 8.50 Na2O 2.35 0.50 0.50 0.70 0.70 0.70 0.70 0.70 0.70 0.70 1.20 0.70 0.70 0.70 2.00 K2O 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.50 0.50 0.50 0.10 MgO 2.00 3.70 3.70 2.50 2.50 2.50 2.00 2.50 6.00 5.50 1.30 1.30 0.50 0.50 0.80 CaO 2.80 2.50 2.50 4.30 4.30 4.30 4.50 3.30 1.50 0.50 3.30 3.50 4.50 5.00 2.00 SrO 0.24 0.80 BaO ZnO 0.11 0.10 0.10 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.15 P2O5 0.26 0.25 0.25 0.27 0.27 0.27 0.27 0.27 0.27 0.27 0.50 0.50 0.50 0.50 0.50 Fe2O3 TiO2 1.00 ZrO2 0.11 0.25 0.25 0.15 0.15 0.15 0.15 0.20 0.20 0.40 0.10 0.10 0.10 0.10 CeO2 0.16 0.15 0.15 0.15 0.15 0.15 0.02 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 SnO2 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.10 SO3 0.03 0.03 0.03 0.03 0.03 F Cl 0.20 0.20 0.55 0.55 0.55 0.55 0.55 0.55 0.55 Properties V1 V2 V3 V4 V5 V6 V7 V8 CTE20-300 5.49 4.77 4.73 4.96 5 5.05 5.18 4.69 [ppm/K] Tg [° C.] 560 586 620 608 581 592 614 601 T2 (from 1697 1691 1649 1620 1663 1619 1569 1703 VFT) [° C.] ρ [g/cm3] 2.404 2.3955 2.4125 2.4191 2.4093 2.4222 2.4268 2.3954 VA [° C.] 1190 1201 1214 1190 1185 1165 1168 1234 T3 [° C.] 1394 1399 1393 1367 1376 1353 1334 1426 VFT A −2.129 −2.178 −2.664 −2.646 −2.278 −2.105 −2.752 −2.567 VFT B 6417.5 6312.1 6760.5 6642.9 6353.3 5810.3 6430.3 7039.4 VFT T0 142.7 179.9 199.0 190.5 178.0 203.2 216.1 162.1 OEG [° C.] 1185 1260 1260 1235 1215 1195 1275 1255 lg (Liquidus 4.03 3.67 3.71 3.71 3.85 3.75 3.32 3.87 Viscosity) [dPa*s] Properties V9 V10 V11 V12 V13 V14 V15 CTE20-300 4.63 4.53 4.91 4.86 4.95 4.99 5.16 [ppm/K] Tg [° C.] 622 585 586 587 585 594 638 T2 (from 1664 1723 1705 1706 1704 1700 1841 VFT) [° C.] ρ [g/cm3] 2.4118 2.3724 2.3826 2.3829 2.3908 2.4004 2.404 VA [° C.] 1219 1224 1217 1217 1213 1210 1328 T3 [° C.] 1402 1426 1415 1415 1412 1408 1539 VFT A −2.603 −2.230 −2.307 −2.257 −2.221 −2.162 −2.580 VFT B 6754.0 6566.9 6624.7 6519.9 6444.4 6285.2 7732.7 VFT T0 196.3 170.2 166.5 174.9 177.3 190.0 152.8 OEG [° C.] 1255 1265 1260 1240 1240 1245 1285 lg (Liquidus 3.78 3.77 3.75 3.86 3.84 3.80 4.25 Viscosity) [dPa*s]

Comparative example V1 has an excessively high coefficient of thermal expansion, so that cooling results in higher stresses which, especially in the case of thin glass, can lead to buckling and/or cracking of the glass.

Comparative example V15 has an excessively high T2 temperature, so that the melt is excessively viscous at the temperatures used in industrial glass production and bubbles are removable only incompletely in the refining step, thus leading to low yield.

Comparative examples V2 to V14 exhibit an unfavorable position of OEG and VA relative to one another. Starting from the hot melt the viscosity range in which crystals may be formed thus begins sooner and the tendency for devitrification is altogether elevated. This is detrimental to producing such a glass with good yields.

The reported OEG, VA, T2 and CTE values for the working examples show that the glass provided according to the invention is very readily processible.

It is producible in good yield, especially also at low thicknesses, for example in the range from 0.3 to 0.7 mm. It does not have a tendency for crystallization. Stresses in the cooling lehr, which easily occur especially in the float process on account of the different cooling of the thin net-product glass and the thick border, can be very largely avoided.

The glass provided according to the invention is very amenable to chemical tempering.

Subjecting samples having the composition of the working examples to ion exchange under the following conditions:

    • ion exchange in an exchange bath having a composition of 20% by weight of KNO3 and 80% by weight of NaNO3 at a temperature of the exchange bath of 420° C. and a duration of 7.5 hours and
    • a further ion exchange in an exchange bath having a composition of 100% by weight of KNO3 and 0% by weight of NaNO3 at a temperature of the exchange bath of 390° C. and a duration of 3 hours,
    • results in the following properties as shown by way of example for exemplary glasses 6, 7, 8 and 9 in the following Table 3, which reports the values not only for CT (=center tension, i.e. tensile strength), CS30, CS50 and DoCL, but also for K—CS and K-DOL:

TABLE 3 Exemplary Glass 6 7 8 9 Glass 0.479 0.477 0.472 0.509 thickness [mm] CS30 137 133 139 154 [MPa] CS50 108 108 115 126 [MPa] DoCL [μm] 111 108 109 117 CT [MPa] 133 135 142 144 K-CS 810 828 810 893 [MPa] K-DOL 3.8 3.6 3.4 3.6 [μm]

The chemically tempered glass provided according to the invention thus has the following properties: CT>80 MPa, optionally CT>100 MPa, CS30>100 MPa, CS50>80 MPa and DoCL>0.17*t.

The glass provided according to the invention in the tempered state is thus very suitable for use as a cover for the recited applications; it combines the good product properties with very good production and processing properties.

While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

Claims

1. A chemically temperable or chemically tempered glass, comprising:

SiO2, Al2O3, Li2O and B2O3 as constituents, characterized in that the following applies for the constituents (in mol % based on oxide): 0.8<Li2O/(Li2O+K2O+Na2O)≤1 and 0.1<B2O3≤8.5.

2. The glass of claim 1, further comprising Na2O and/or K2O.

3. The glass of claim 1, characterized in that:

an upper devitrification temperature OEG is less than 10 K above a processing temperature VA;
a temperature at a viscosity of 102 dPas is at most 1800° C.; and
a coefficient of thermal expansion CTE20-300 is less than 5.4 ppm/K.

4. The glass of claim 1, wherein the glass comprises the following constituents (in mol % based on oxide): SiO2 62-72; Al2O3 7-14; B2O3 0.1-8.5; Li2O 5-12; Na2O 0-2; and K2O 0-2.

5. The glass of claim 4, wherein the glass comprises the following constituents (in mol % based on oxide): SiO2 65-70; Al2O3 8-12; B2O3 4-7; Li2O 7-10; Na2O 0-1; and K2O 0-1.

6. The glass of claim 1, wherein the glass further comprises the following constituents (in mol % based on oxide): MgO 0-5; CaO 0-8; SrO 0-5; BaO 0-2; ZnO 0-5; P2O5 0-5; and ZrO2 0-5.

7. The glass of claim 6, wherein the glass comprises the following constituents (in mol % based on oxide): MgO 0.5-3; CaO 1-6; SrO 0-1; BaO 0-2; ZnO 0-1; P2O5 0.5-2; and ZrO2 0-3.

8. The glass of claim 6, characterized in that the following applies for the constituents (in mol % based on oxide):

0.9<(Al2O3+B2O3+ZrO2)/(R2O+RO)<1.7; and/or
0.5<Al2O3/(R2O+RO)<1.1; wherein R2O=Li2O+K2O+Na2O and RO=MgO+CaO+SrO+BaO+ZnO.

9. The glass of claim 8, wherein 1<(Al2O3+B2O3+ZrO2)/(R2O+RO)<1.6 and/or 0.6<Al2O3/(R2O+RO)<0.9.

10. The glass of claim 1, wherein the glass contains 0 to 1 mol % of SnO2 and/or 0 to 1 mol % of CeO2, and/or 0 to 1 mol % of Cl.

11. The glass of claim 10, wherein the glass contains 0.1 to 0.5 mol % of SnO2.

12. The glass of claim 10, wherein a sum of CeO2+SnO2+Cl is at most 2 mol %.

13. The glass of claim 1, wherein the glass is substantially free from coloring components.

14. The glass of claim 1, wherein the glass contains at least 0.1 mol % and at most 5 mol % of at least one coloring component.

15. A process for producing a tempered glass, the glass comprising SiO2, Al2O3, Li2O and B2O3 as constituents, wherein the following applies for the constituents (in mol % based on oxide): 0.8<Li2O/(Li2O+K2O+Na2O)≤1 and 0.1<B2O3≤8.5, the method comprising:

producing the glass by a melting process, a refining of a glass melt produced during the melting process, and a subsequent hot forming; and
performing at least one ion exchange in an exchange bath having a composition of 100% by weight to 0% by weight of KNO3 and 0% by weight to 100% by weight of NaNO3 and 0% by weight to 5% by weight of LiNO3 at a temperature of the exchange bath between 370° C. and 500° C. and a duration between 1 hour and 50 hours.

16. The process of claim 15, wherein the hot forming is carried out by a drawing process comprising a float process or a down-draw process.

17. A cover, comprising:

a tempered glass having a thickness of 0.3 mm to 1 mm, the glass comprising SiO2, Al2O3, Li2O and B2O3 as constituents, characterized in that the following applies for the constituents (in mol % based on oxide): 0.8<Li2O/(Li2O+K2O+Na2O)≤1 and 0.1<B2O3≤8.5.

18. The cover of claim 17, wherein the glass further comprises Na2O and/or K2O.

19. The cover of claim 17, characterized in that:

an upper devitrification temperature OEG of the glass is less than 10 K above a processing temperature VA of the glass;
a temperature at a viscosity of 102 dPas of the glass is at most 1800° C.; and
a coefficient of thermal expansion CTE20-300 of the glass is less than 5.4 ppm/K.

20. The cover of claim 17, wherein the glass comprises the following constituents (in mol % based on oxide): SiO2 62-72; Al2O3 7-14; B2O3 0.1-8.5; Li2O 5-12; Na2O 0-2; and K2O 0-2.

Patent History
Publication number: 20250083992
Type: Application
Filed: Sep 5, 2024
Publication Date: Mar 13, 2025
Applicants: Schott AG (Mainz), SCHOTT Technical Glass Solutions GmbH (Jena)
Inventors: Sebastian Leukel (Mainz), Patrick Wilde (Mainz), Eric Oberländer (Jena)
Application Number: 18/825,608
Classifications
International Classification: C03C 3/11 (20060101); C03C 4/02 (20060101); C03C 21/00 (20060101); H05K 5/03 (20060101);